Pressure operated electric switches



y 1964 R. G. PANNELL 3,140,369

PRESSURE OPERATED ELECTRIC SWITCHES Filed Aug. 3, 1961 l2 l6 8 I 9 R IO 16 l I3 9 I4 20 N /7 8 I5 E I, 65a

INVENTOR passer GEOPGE pA/VNELL 4 h /MW United States Patent 3,140,369 PRESSURE OPERATED ELECTRIC SWITCHES Robert G. Pannell, Gosport, England, assignor of one-half to Graviner Manufacturing Company Limited, and onehalf to Wilkinson Sword Limited, both of London, England, both British companies a Filed Aug. 3, 1961, Ser. No. 129,154 Claims priority, application Great Britain Aug. 16, 1960 3 Claims. (Cl. 200-83) This invention relates to pressure responsive devices and particularly, but not exclusively, to switches of the kind having electrical contacts whose state of operation is changed by a predetermined change of pressure or by a predetermined rate of rise of pressure.

Difficulties arise with known switches because'although they may be set to operate at a predetermined pressure, the setting of the switch varies with temperature. This has the result that operation of the switch, for example closure of the contacts in the case of an electric switch, occurs at a substantially dilferent pressure at temperatures ditierent from that at which the switch was set. expansion of the components of the switch.

According to the present invention there is provided a pressure responsive device having two members the separation between which is dependent upon the pressure to which the device is subjected, wherein a bimetallic member is used to compensate, at least partially, for variations in said separation which would otherwise occur with variations in temperature due todifferential thermal expansion of the supporting members on which said two members are mounted.

The invention also provides a pressure responsive device having a diaphragm and two electrical contacts the separation between which is dependent upon the pressure on the diaphragm, differential thermal expansion of the supporting members by which said contacts are mounted in said device tending to vary the separation of said contacts at any given pressure, wherein a bimetallic member is fitted in said device to oppose, at least partially variation in the separation of said contacts, due to said diiferential thermal expansion.

The invention further provides a pressure responsive device having a diaphragm and two electrical contacts, said contacts being adapted to engage when said diaphragm is exposed to a predetermined pressure, one of said contacts being movable with said diaphragm and the other, of said contacts being movable with a bimetallic member which is responsive to the temperature to whichthe device is subjected, the arrangement being such that deviations, in the pressure at which said contacts engage, from said predetermined pressure as a result of variations in. temperature are opposed by movement of said bi-metallic member.

One construction of pressure responsive device in accordance with the invention, will not be described, by way of example only, with reference to the accompanying drawing which is a sectional side elevation of the switch.

Referring now to the drawing, the switch comprises 7 a cylindrical terminal box 1 closed at one end by a mounting flange 2 and at the other end by a cover 3. The outer face of the mounting flange 2 is recessed and a corrugated metal diaphragm 4 extends across the recessed portion with the periphery of the diaphragm 4 welded to the mounting flange 2. A vacuum support 5 is secured to the center of the diaphragm 4 and extends through a centrol hole in the mounting flange 2. The vacuum support 5 is provided with a flange 5a which prevents the diaphragm 4 being displaced outwardly by partial vacuum to a greater extent than that which This is caused primarily by thermal 3,140,369 Patented July '1, H1964 brings the flange 5a into engagement with the mounting flange 2. The vacuum support 5 carries a stand-off insulator 6 on which is mounted a contact holder 7 carrying a contact 8. The contact 8 is electrically connected by an insulated braided wire 9 to a terminal bolt 10 which at one end is secured in an insulating bushing 11 in an aperature in the mounting flange 2 and at the other end extends through an annular insulating terminal plate 12 to provide a terminal to which an electrical connection can be made. The terminal plate 12 is supported from the mounting flange 2 by a bridge 13 which is itself secured to the inner face of the mounting flange 2. A second electrical contact 14 is mounted on a bi-metallic disc 15 which is clamped in a holder 16 by a clamping nut 17, the arrangement being such that the center of the disc 15 can move unimpeded. The holder 16 for the bi-metallic disc 15 is supported by its stem 16a which extends through a pressure setting adjustment member 18 and is insulated therefrom by insulating bushings 19. The periphery of the adjustment member 18 is screw threaded and engages the screw-threaded periphery of a central hole in the bridge 13 so that the gap between the contacts 8 and 14 can be adjusted by rotation of the member 18 relative to the bridge 13. After adjustment the member 18 is locked against rotation relative to the bridge 13 by a locking screw 20. The upper end of the stem 16a of the disc-holder 16 is screw-threaded to provide a terminal to which an electrical connection can be made. An external circuit can then be connected to the ter- .minals of terminal bolt 10 and stem 16a so that on closure of the contacts 8 and 14 an electrical circuit can be completed to eifect any desired operation, which may for example be discharged of explosion suppressing fluid to suppress an incipient explosion which has caused the pressure rise resulting in closure of the contacts. It will be understood that the switch can readily be adapted so that an increase in pressure causes opening of normally closed contacts.

Pressure responsive devices according to the invention may be used in chemical plants and similar installations in which liquids, fluids and gases may be handled which are corrosive or not compatible with certain metals. According to the installation the diaphragm may be iron, steel or ferrous alloys, particularly stainless steel, of copper or copper alloy such as beryllium copper or of pure aluminium or aluminium alloy. The switch casings and other parts may be of cast iron or steel, of copper alloys or bronzes or of aluminium or aluminium alloys.

As a result the differential thermal expansion between the components of the switch depends upon the particular materials used. The necessary temperature compensation can be provided. by deflection of the bimetallic disc 15 with variations of temperature, this deflection compensating for the relative movement which would otherwise occur between the contacts 8 and 14 due to thermal expansion of the other components of the switch. The deflection of the disc 15 also compensates for the fact that the diaphragm 4 is also affected by temperature, because for a given pressure applied to it the diaphragm will move further at high temperatures than at lower temperatures.

This is achieved by varying the effective diameter of bi-metallic disc 15 in dependence upon the combination of materials employed. The disc 15 is clamped around its periphery by nut 17 and holder 16, which is recessed so that the central portion of the disc 5 is free to flex as the result of temperature changes; trapping of air in the recess is avoided by the provision of an air relief hole. The amount to which the recess is machined out depends upon the combination of materials employed for the switch and is so chosen that the deflection of the disc 15 with variations of temperature automatically maintains the distance between contacts 8 and 14 as nearly constant as possible over a wide range of temperature, for example from below normal room temperature to above 100 C.

This facility for varying the active (or unclamped) portion of disc 15 also permits the use of different types and thickness of commercially available types of bimetallic material, as well as of the use of commercially available materials for the switch casing, diaphragm and other parts thereby reducing production costs.

Needless to say the invention may be applied to other devices in which it is important to ensure that electrical contacts remain uniformly spaced if the devices are subjected to temperature changes which may alter the distance between the contacts.

It may be stated that with such a switch set to operate at a pressure of 0.25 p.s.i.g. the setting was maintained approximately constant with variation of temperature from 25 C. up to 250 C. whereas without the use of the bi-metallic disc the temperature setting decreased from 0.25 p.s.i.g. at 25 C. to 0.15 p.s.i.g. at 225 C.

A switch having the construction shown can readily be set to operate over a range of to p.s.i.g. by the use of diaphragms and bi-metallic discs of different thicknesses for different portions of the range.

I claim:

1. A pressure-sensitive electric switch comprising a housing, said housing having two ends one of which is closed and the other having an opening therein, a circular diaphragm, said diaphragm having its periphery sealed to said housing with the diaphragm extending across said opening, a first electrical contact secured to said diaphragm lying within said housing, a temperature responsive bi-metallic disc, a second electrical contact centrally mounted on said bi-metallic disc, a bridge-piece supported by said housing, and means for clamping the periphery of said bi-metallic disc, said clamping means being secured to said bridge-piece with said second electrical contact adjacent and spaced from said first electrical contact, the clamping means and bridge-piece being in screwthreaded engagement whereby the separation between said first and second electrical contacts may be selectively varied, flexing of said bi-metallic disc with a change in ambient temperature compensating at least partially for relative movement which would otherwise occur between said first and second electrical contacts as a result of the flange, a first electrical contact, a supporting member for said first electrical contact, said supporting member being mounted on said diaphragm and extending through said central hole, said first electrical contact being mounted on said supporting member and lying within the interior of said housing, said supporting member having a flanged portion, whereby movement of said diaphragm away from said mounting flange is limited by engagement of said flanged portion of said supporting member with said mounting flange, a second electrical contact, and a bimetallic member, said bi-metallic supporting member being secured to said mounting flange, said second electrical contact being supported by said bi-metallic member in juxtaposition to said first electrical contact, whereby flexing of said bi-metallic member with a change in the ambient temperature compensating at least partially for relative movement which would otherwise occur between said first and second electrical contacts consequent upon the thermal expansion of said housing and said mounting flange due to said change in ambient temperature.

3. A pressure-responsive electric switch comprising an open-ended cylindrical housing, a cover secured to said housing and extending across one end of said housing, a mounting flange, said mounting flange being secured to said housing across the end opposite to the end across which said cover extends, said mounting flange having a central hole, a diaphragm secured to said mounting flange, a first electrical contact, a supporting member for said first electrical contact, said supporting member being mounted on said diaphragm and extending through said central hole, said first electrical contact being mounted on said supporting member and lying within the interior of said housing, a bridge-piece mounted on said mounting flange and lying within the interior of said housing, a bimetallic disc, a second electrical contact centrally mounted on said bi-metallic disc at a greater distance from said diaphrgarn thansaid first electrical contact, and means for supporting said bi-metallic disc, said bi-metallic disc supporting means clamping the periphery of said bi-metallic disc, said bi-metallic disc supporting means being in screwthreaded engagement with said bridge-piece, whereby the separation between said first and second electrical contacts may be selectively varied, flexing of said bi-metallic disc with temperature variations compensating at least partially for relative movement which would otherwise occur between said first and second electrical contacts consequent upon thermal expansion of said housing, said bridge piece and said bi-metallic disc supporting means.

References Cited in the file of this patent UNITED STATES PATENTS 1,954,142 Motfett Apr. 10, 1934 2,279,140 Kellen Apr. 7, 1942 2,454,288 Michaelson Nov. 23, 1948 2,736,970 Engel Mar. 6, 1956 2,791,655 Gilbert May 7, 1957 2,873,328 Hainy Feb. 10, 1959 2,978,879 Heidorn Apr. 11, 1961 u J Han. 

1. A PRESSURE-SENSITIVE ELECTRIC SWITCH COMPRISING A HOUSING, SAID HOUSING HAVING TWO ENDS ONE OF WHICH IS CLOSED AND THE OTHER HAVING AN OPENING THEREIN, A CIRCULAR DIAPHRAGM, SAID DIAPHRAGM HAVING ITS PERIPHERY SEALED TO SAID HOUSING WITH THE DIAPHRAGM EXTENDING ACROSS SAID OPENING, A FIRST ELECTRICAL CONTACT SECURED TO SAID DIAPHRAGM LYING WITHIN SAID HOUSING, A TEMPERATURE RESPONSIVE BI-METALLIC DISC, A SECOND ELECTRICAL CONTACT CENTRALLY MOUNTED ON SAID BI-METALLIC DISC, A BRIDGE-PIECE SUPPORTED BY SAID HOUSING, AND MEANS FOR CLAMPING THE PERIPHERY OF SAID BI-METALLIC DISC, SAID CLAMPING MEAN BEING SECURED TO SAID BRIDGE-PIECE WITH SAID SECOND ELECTRICAL CONTACT ADJACENT AND SPACED FROM SAID FIRST ELECTRICAL CONTACT, THE CLAMPING MEANS AND BRIDGE-PIECE BEING IN SCREWTHREADED ENGAGEMENT WHEREBY THE SEPARATION BETWEEN SAID FIRST AND SECOND ELECTRICAL CONTACTS MAY BE SELECTIVELY VARIED, FLEXING OF SAID BI-METALLIC DISC WITH A CHANGE IN AMBIENT TEMPERATURE COMPENSATING AT LEAST PARTIALLY FOR RELATIVE MOVEMENT WHICH WOULD OTHERWISE OCCUR BETWEEN SAID FIRST AND SECOND ELECTRICAL CONTACTS AS A RESULT OF THE AMBIENT TEMPERATURE CHANGE CAUSING THERMAL EXPANSION OF SAID HOUSING, SAID BRIDGE-PIECE AND SAID CLAMPING MEANS. 